feat: Enable synchronous screen shadow state updates by default

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: kmichalikk

FabricExample/App.tsx

@@ -1,7 +1,7 @@
 import App from '../apps';
 import { featureFlags } from 'react-native-screens';
 
-featureFlags.experiment.synchronousScreenUpdatesEnabled = false;
+featureFlags.experiment.synchronousScreenUpdatesEnabled = true;
 featureFlags.experiment.synchronousHeaderConfigUpdatesEnabled = true;
 featureFlags.experiment.synchronousHeaderSubviewUpdatesEnabled = true;
 featureFlags.experiment.androidResetScreenShadowStateOnOrientationChangeEnabled =

ios/RNSScreen.mm

@@ -103,6 +103,7 @@ - (void)initCommonProps
   _sheetsScrollView = nil;
   _sheetContentHeight = 0.0;
   _markedForUnmountInCurrentTransaction = NO;
+  _synchronousShadowStateUpdatesEnabled = YES;
 }
 
 + (RNSViewInteractionManager *)viewInteractionManagerInstance

src/fabric/ModalScreenNativeComponent.ts

@@ -121,7 +121,7 @@ export interface NativeProps extends ViewProps {
   leftScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   rightScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   topScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
-  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, false>;
+  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, true>;
 }
 
 export default codegenNativeComponent<NativeProps>('RNSModalScreen', {

src/fabric/ScreenNativeComponent.ts

@@ -121,7 +121,7 @@ export interface NativeProps extends ViewProps {
   leftScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   rightScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
   topScrollEdgeEffect?: CT.WithDefault<ScrollEdgeEffect, 'automatic'>;
-  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, false>;
+  synchronousShadowStateUpdatesEnabled?: CT.WithDefault<boolean, true>;
   androidResetScreenShadowStateOnOrientationChangeEnabled?: CT.WithDefault<
     boolean,
     true

src/flags.ts

@@ -1,4 +1,4 @@
-const RNS_SYNCHRONOUS_SCREEN_STATE_UPDATES_DEFAULT = false;
+const RNS_SYNCHRONOUS_SCREEN_STATE_UPDATES_DEFAULT = true;
 const RNS_SYNCHRONOUS_HEADER_CONFIG_STATE_UPDATES_DEFAULT = true;
 const RNS_SYNCHRONOUS_HEADER_SUBVIEW_STATE_UPDATES_DEFAULT = true;
 const RNS_ANDROID_LEGACY_TOP_INSET_BEHAVIOR_DEFAULT = false;
@@ -195,6 +195,11 @@ export const featureFlags = {
    *  Flags to enable experimental features. These might be removed w/o notice or moved to stable.
    */
   experiment: {
+    /**
+     * Enables synchronous shadow state updates for Screen components on iOS
+     * (Fabric, RN 0.82+). On by default.
+     * PR: https://github.com/software-mansion/react-native-screens/pull/3282
+     */
     get synchronousScreenUpdatesEnabled() {
       return synchronousScreenUpdatesAccessor.get();
     },